This invention concerns an artificial ligament in synthetic material coated with elastic resin as well as the procedure for manufacture of this ligament.
Articular accidents are well-known, notably amongst sporting people, such as tearing or rupture of a ligament; it is also known that in such cases, some of the damaged ligaments cannot reconstitute themselves.
The present-day recognised solution consists of the replacement of the fractured ligament by a prosthetic ligament inserted by classical surgical methods.
In this type of operation, prosthetic ligaments manufactured from synthetic fibres are most frequently used. These fibres are arranged longitudinally to constitute a resistant core of a tube of synthetic textile ensuring the mechanical holding of the whole.
With a suitable length and diameter in relation to the damaged ligament which they are designed to replace, the tube of textile fibres thus constituted undeniably demonstrates a satisfactory mechanical resistance under traction.
However, it can be observed that a piling up of the fibres arranged longitudinally, if it were to satisfy, in the desired proportions, the constraints of traction which in first class ligament implant requires, cannot on the other hand bear any traction overload without risk of permanent deformity. It is well understood in fact that subsequent to an unusual effort of traction, even momentary, on an artificial ligament of the type previously described, the longitudinally placed fibres undergo a relative axial displacement, which nothing can reasonably prevent, the fibres being able to slide one against the other. The risk of establishing an irreversible deformation of the artificial ligament is therefore great.
All the above can be summarised by saying that the artificial ligaments currently available, even if they give good guarantees of resistance to the normal efforts of articulation common to such prostheses, have only a very mediocre capacity to withstand any violent constraint, even passing and accidental.
Moreover, it can frequently be observed that an implantation of an artificial ligament is rejected by the patient's body and undesirable reactions are often to be feared because they are the result of direct contact of the artificial fibres with the biological environment.
Some previous versions are already known, such as the solution described in the patent, FR-A-2135825, in which the manufacture of a tendon from a snap-proof band of knitted polyester fibre arranged at the interior of an independent sheath in elastomer band is proposed. This version produces the characteristic of longitudinal inextensibility and ensures improved smooth running of the band within its elastomer sheath, which is, in principal, the desired function for a tendon which links a muscle to a bone.
Similarly known is, the subordinate solution proposed by the patent, U.S. Pat. No. 3,545,008, which recommends coating the tendons and artificial ligaments with a biocompatible elastomer resin, in such a manner as to isolate the central core from the biological environment and avoid any rejection; as in the previously mentioned french patent, coating the artificial tendon with an elastomer resin furthermore facilitates the smooth running of the tendon in its specific movements.
The patent, EP-A-0051945 is also known in which a particular method of manufacture or a tendon or prosthetic ligament using elastomers is described, as much for the mechanical holding between the fibres, procuring various conformations of the prosthesis in the manner of its applications, as for assuring biocompatibility of the aforesaid implanted prosthesis.
In all these previous versions using a combination of knitted textiles, coated with elastomer, no mention is made of the problem of longitudinal deformations of ligaments undergoing a momentary effort which may, furthermore, be violent in the case of people involved in competitive sports for example.
In conclusion, it is known that a biological ligament can undergo an extension of 30 percent before rupture corresponding to an effort of around 2,000 Newtons and that in general it gives the individual a reserve of reversible extensibility, during a sustained effort corresponding to 1,000 Newtons, of about 18 percent without any damage caused to the aforesaid ligament.